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Opera&onAmplifiers(OpAmps)

•  Ac&vedevice,capableofprovidingvoltagegain

•  Withproperconfigura&on,canimplementsumming,subtrac&on,integra&ononinputsignals

•  Usedinnearlyeveryelectronicdevice

•  Nearlyalwaysusedinafeedbackconfigura&on

+Differen&alinputs -

Single-endedOutput

V(+)

V(-)Vo

Feedback Network

i(+)

i(-)

•  Wewilltreatthisdeviceasabuilding“block”withspecific(ideal)aJributesknownastheGOLDENRULESofOp-amps:

-  Infiniteinputimpedanceonthe+and–terminalsi(+)=i(-)=0.

-  VochangessothatV(+)=V(-)atall&mes…thismeanstheop-ampsourcesorsinkscurrentattheoutputterminalthroughthefeedbacknetworksothatV(+)=V(-).

Exampleofcircuitanalysiswithop-amps

Vout

RfRG

Vin

+15

-15

PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp…Nowconsider:

Vout

Rf

RG

Vin

1.  Usingouridealop-ampcharacteris&csfindanexpressionforVout/Vin

2.  Whatopera&ondoesthisop-ampconfigura&onperform?

3.  List(atleast3)possibledevia&onsfromtheidealop-ampmodelandhowthosedevia&onsaffectyourresultfromexpression1.

+15

-15

ENPH259GroupAc&vi&esforOct52017

Vout

Rf

RG

Vin

1.  Usingouridealop-ampcharacteris&csfindanexpressionforVout/Vin

+15

-15

PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp

ENPH259GroupAc&vi&esforOct52017

PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp

ENPH259GroupAc&vi&esforOct52017

…Nowconsider:

Vout

Rf

RG

Vin

2.  Whatopera&ondoesthisop-ampconfigura&onperform?

+15

-15

Actslikeanon-inver&ngamplifierwithgain>1

PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp

ENPH259GroupAc&vi&esforOct52017

PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandandEmilyorDavidwillcometohelp

Vout

Rf

RG

Vin

3.  List(atleast3)possibledevia&onsfromtheidealop-ampmodelandhowthosedevia&onsaffectyourresultfromexpression1.

-15

Gainischanged

Gainischanged

ENPH259GroupAc&vi&esforOct82015PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp

ENPH259GroupAc&vi&esforOct52017

+15

Vout

Rf

RG

Vin

+15

-15

3.  List(atleast3)possibledevia&onsfromtheidealop-ampmodelandhowthosedevia&onsaffectyourresultfromexpression1.

PleasecompletetheseexercisesonyourOWNpieceofpaper.Ifyouhaveques&onstalkwithyourgroupmatesorraiseyourhandDavidwillcometohelp

ENPH259GroupAc&vi&esforOct52017

15

Vout

RFRG

Vin

+15

-15

G =Vout

Vin

= �RF

RG

Twoofthemostimportantnon-idealaspectsofop-ampsare:

•  Thegainisnotinfinite

•  Themaximumgainwhichcanbeproducedisafunc&onoffrequency.Inotherwords,GdependsondrivefrequencyofVin

Hereisanexampleofanon-idealmodelofanOpAmpusingavoltage-dependentvoltagesource.

TheOpAmpcan’tmakeVoutarbitrarilylargebecauseAisnotinfinite.ThismeanstherewillalwaysbeasmallVd.

StartonPrelabfornextweekENPH259GroupAc&vi&esforOct52017